Metallic containers are frequently decorated with an image or indicia, such as a brand name, logo, product information, or design, using a lithographic printing process. In lithographic printing, one or more printing plates (or primary plates) with image regions are attached to a plate cylinder (or press cylinder) of a decorator. The image regions can include both ink receiving regions and areas that do not receive ink. An inker applies ink to the printing plates and the ink adheres to the ink receiving regions. Usually each printing plate receives a particular color of ink from the inker. The decorator also has a blanket cylinder (also known as an offset cylinder, a printing cylinder, or a segment wheel). Secondary plates (or secondary transfer plates or printing blankets) are attached to the blanket cylinder. Decorators used in the metallic container industry typically have from 4 to 12 secondary plates on the blanket cylinder. As the plate cylinder and blanket cylinder are rotated in unison, each of the one or more printing plates contacts a secondary plate and transfers a particular color of ink to the secondary plate. When all of the printing plates have transferred their ink colors and images to the secondary plate, the final lithographic image is formed on the secondary plate. A cylindrical metallic container is then brought into rotational contact with one of the secondary plates of the blanket cylinder and the lithographic image is transferred from the secondary plate to the exterior surface of the cylindrical metallic container.
Lithographic printing methods are generally described in U.S. Pat. Nos. 3,766,851, 4,384,518, 6,550,389, and 6,899,998, each of which are incorporated herein by reference in their entireties. The methods described in these references generally only allow a single lithographic image to be produced from a single set of printing plates. Thus, the methods described in these patents are only efficient for printing the same image onto a large number of cylindrical metallic containers. In order to print a different image on a plurality of cylindrical metallic containers, a new set of printing plates must be installed on the plate cylinder of the decorator, resulting in downtime and decreased efficiency of a production line. Because only one image can be printed without changing the printing plates, it is economically challenging to produce small batches of decorated cylindrical metallic containers with different images.
One example of providing multiple different images from a single set of printing plates is provided in U.S. Pat. No. 5,181,471 to Sillars, which is incorporated herein by reference in its entirety. Sillars generally describes a printing system with engraved images formed in flexographic regions of secondary plates attached to the blanket cylinder.
Another method of providing multiple distinct images using a single set of printing plates is described in International Patent Publication No. WO 2014/008544 by Treloar, which is incorporated herein by reference in its entirety. Treloar generally describes a blanket cylinder with secondary plates that are adapted to have inked regions and non-inked regions. Other methods of providing multiple distinct images in lithographic printing processes are described in International Patent Publication No. WO 2014/006517 by Vilas Boas et al. (Vilas Boas) and International Patent Publication No. WO 2014/128200 by Grahame et al. (Grahame), each of which are incorporated herein by reference in their entireties. However, the lithographic images described by Sillars, Treloar, Vilas Boas, and Grahame using these various techniques do not have sufficient detail to be considered a high quality, high-definition image. Further, none of these patents or patent publications describes the use of specialty inks in the printing process or novel materials used for the secondary plates to create high image quality in a mass production process. The commercial metallic container industry requires high-definition printing in unique applications and requires distinct graphical elements formed by specialty inks that can efficiently be printed with high resolution and detail on the exterior surface of a cylindrical metallic container. These high-definition images and the use of specialty inks are necessary to differentiate products at the point of sale and to attract consumers.
U.S. Patent Application Publication 2014/0210201 to Owen et al. (Owen), which is incorporated by reference herein in its entirety, generally describes the use of thermochromic and photochromic inks to decorate beverage cans. However, Owen teaches the use of ink jet printing to apply the inks to the cans which is generally a slow and non-economical process. In contrast, the commercial container industry requires an apparatus and method capable of decorating beverage containers at significant production speeds of at least several thousand cylindrical metallic containers per minute.
Accordingly, there is an unmet need for a high-definition lithographic printing process that allows multiple images to be printed on an exterior surface of a cylindrical metallic container from a single set of printing plates and secondary plates that uses specialty inks and/or improved plate materials without sacrificing production efficiency or image quality and detail.